The ASTRA (Ancient instruments Sound/Timbre Reconstruction Application) is a project coordinated at Conservatory of Music of Parma which aims to reconstruct the sound or timbre of ancient instruments (not existing anymore) using archaeological data as fragments from excavations, written descriptions, pictures.

The technique used is the physical modeling synthesis, a complex digital audio rendering technique which allows modeling the time-domain physics of the instrument.

In other words the basic idea is to recreate a model of the musical instrument and produce the sound by simulating its behavior as a mechanical system. The application would produce one or more sounds corresponding to different configurations of the instrument (i.e. the different notes).

To model ancient instruments not existing anymore ASTRA used a technique called physical modeling. The physical modelling sound synthesis technique aims in fact to use a set of equations and algorithms that describe the physical materials used in the ancient instruments to generate physical source of sound. In other words, the basic idea is to recreate a model of the musical instrument and produce the sound by simulating its behavior as a mechanical system. This would lead to a natural synthesized sound, correctly reproducing the instrument mechanics.

For example, to model the sound of a drum, a formula for how striking the drumhead injects energy into a two dimensional membrane would be created. Then, the properties of the membrane (mass density, stiffness, and so on), its coupling with the resonance of the cylindrical body of the drum, and the conditions at its boundaries (a rigid termination to the drum's body) would describe its movement over time and how it would sound.

Similar modelling can be carried out in instruments such as a violin, though replicating the slip-stick behavior of the bow against the string, the width of the bow, the resonance and damping behavior of the strings, the transfer of string vibrations through the bridge, and finally, the resonance of the soundboard in response to those vibrations.

It is possible to say then that an instrument model within ASTRA, consists of laws of physics that govern the sound production and evolution, and will typically have several parameters, some of which are constants that describe the physical materials and dimensions of the instrument, while others are time-dependent functions that describe the player's interaction with it, such as plucking a string, or covering tone holes.

The ASTRA project uses regularly archaeological data as input (for example fragments from excavations, written descriptions, pictures on ancient urns), so that the complex digital audio rendering technique was tuned to models the sound of the particular instrument under study. The models used by ASTRA are validated by engineers and historians, before being translated in software programs running on hundreds of computers in Europe and in the lower Mediterranean area, generating the actual sounds of the instruments.

To bring together sufficient power and to share information among the people involved in project, we are using the GILDA (https://gilda.ct.infn.it) and EUMEDGRID (www.eumedgrid.eu) grid computing infrastructures, which link computing resources across the Mediterranean at high speed (up to 2.5 Gbps) through the GÉANT2 (www.geant2.net) and EUMEDCONNECT (www.eumedconnect.net) research networks.

GILDA and EUMEDGRID are part of a bigger project called EGEE (www.eu-egee.org), Enabling Grids for E-sciencE, the largest multi-disciplinary grid infrastructure in the world, which brings together more than 140 institutions as global research community. At present, it gives its 10,000 users access to 80,000 computers in 50 countries.

The physical modelling process needs, in fact, extreme amounts of computing power taking about four hours for a high powered computer to correctly reproduce a sound lasting only 30 seconds. More information are available on the ASTRA project website: www.astraproject.org